Control of Abnormally Oriented Grains (AOG) in Al x Sc 1–x N Bimorph Stack and Characterization of Piezoelectric Properties on an 8-in Wafer

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Piezoelectric MEMS devices based on bimorph scandium-doped aluminum nitride (AlScN) exhibit greater performance potential than those based on unimorph structures. In this paper, we present an optimized bimorph stack utilizing AlxSc${}_{1-\text {x}}$N on an 8-inch silicon wafer. The control of abnormally oriented grains (AOG) was achieved by incorporating Al0.9Sc0.1N and Al0.8Sc0.2N composite films. XRD, TEM, EBSD, and PFM analyses were performed to characterize the proposed composite films. The capacitance ($C_{0}$) and piezoelectric coefficients ($d_{33,f}$) of the fabricated composite bimorph stack were measured using a double beam laser interferometer (DBLI) at the wafer level. Additionally, the relative dielectric constant (${\varepsilon }_{r}$) and intrinsic electromechanical coupling coefficient ($K_{t}^{2}$) were calculated. Results indicate that the Al0.9Sc0.1N and Al0.8Sc0.2N composite bimorph stack exhibits a lower density of AOGs, improved uniformity in$d_{33,f}$(34.8%) and lower stress range (less than 80MPa) across the wafer compared to the pure Al0.8Sc0.2N bimorph stack. Furthermore, the reductions in$d_{33,f}$(10.5%),$K_{t}^{2}$(9.8%), and$\varepsilon _{r}$(6.4%) in the composite bimorph stack remain within acceptable limits. The AlxSc${}_{1-\text {x}}$N bimorph stack with uniformity enhanced by the use of composite films offers a promising solution for the mass production of high-performance piezoelectric MEMS devices.[2025-0074]

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